Geng Zhiyuan, Yan Penji, Wang Yongcheng, Yao Xiaoqiang, Han Yanxia, Liang Junxi
Gansu Key Laboratory of Polymer Materials, College of Chemistry and Chemical Engineering Northwest Normal University, Lanzhou 730070, PR China.
J Phys Chem A. 2007 Oct 4;111(39):9961-8. doi: 10.1021/jp0732211. Epub 2007 Aug 31.
A computational study of the platinum-catalyzed cyclopropanation reaction with olefin is presented. The model system is formed by an ethylene molecule and the active catalytic species, which forms from a CH2 fragment and the Cl2Pt(PH3)2 complex. The results show that the active catalytic species is not a metal-carbene of the type (PH3)2Cl2Pt=CH2 but two carbenoid complexes which can exist in almost two degenerate forms, namely (PH3)2Pt(CH2Cl)Cl (carbenoid A) and (PH3)Pt(CH2PH3)Cl2 (carbenoid B). The reaction proceeds through three pathways: methylene transfer, carbometalation for carbenoid A, and the reaction of a monophosphinic species for carbenoids (A and B). The most favored reaction channel is methylene transfer pathway for (PH3)Pt(CH2PH3)Cl2 (carbenoid B) species with a barrier of 31.32 kcal/mol in gas phase. The effects of dichloromethane, THF, and benzene solvent are investigated with PCM method. For carbenoid A, both methylene transfer and carbometalation pathway barriers to reaction become remarkably lower with the increasing polarity of solvent (from 43.25 and 52.50 kcal/mol for no solvent to 25.36 and 38.53 kcal/mol in the presence of the dichloromethane). In contrast, the reaction barriers for carbenoid B via the methylene transfer path hoist 6.30 kcal/mol, whereas the barriers do not change significantly for the reaction path of a monophosphinic species for carbenoids (A and B).
本文介绍了铂催化烯烃环丙烷化反应的计算研究。模型体系由乙烯分子和活性催化物种构成，该活性催化物种由一个CH₂片段和Cl₂Pt(PH₃)₂配合物形成。结果表明，活性催化物种不是(PH₃)₂Cl₂Pt=CH₂类型的金属卡宾，而是两种类卡宾配合物，它们几乎以两种简并形式存在，即(PH₃)₂Pt(CH₂Cl)Cl（类卡宾A）和(PH₃)Pt(CH₂PH₃)Cl₂（类卡宾B）。反应通过三条途径进行：亚甲基转移、类卡宾A的碳金属化以及类卡宾（A和B）的单膦物种反应。最有利的反应通道是(PH₃)Pt(CH₂PH₃)Cl₂（类卡宾B）物种的亚甲基转移途径，在气相中的势垒为31.32 kcal/mol。采用PCM方法研究了二氯甲烷、四氢呋喃和苯溶剂的影响。对于类卡宾A，随着溶剂极性的增加（从无溶剂时的43.25和52.50 kcal/mol到二氯甲烷存在时的25.36和38.53 kcal/mol），亚甲基转移和碳金属化反应途径的势垒都显著降低。相比之下，类卡宾B通过亚甲基转移途径的反应势垒升高了6.30 kcal/mol，而类卡宾（A和B）的单膦物种反应途径的势垒没有显著变化。
